Slotted waveguide antenna



Sept. 17, 1957 O. M. WOODWARD, JR

SLOTTED WAVEGUIDE ANTENNA Filed July 27, 1953 2 Sheet s-Sheet 1 H? IIUnited States Patent SLOTTED WAVEGUIDE ANTENNA Oakley M. Woodward, Jr.,Princeton, N. 1., assignor to Radio Corporation of America, acorporation of Delaware Application July 27, 1953, Serial No. 370,423

11 Claims. (Cl. 343-771) This invention relates to antennas, andparticularly pertains to an ultra-high-frequency antenna array utilizingslotted waveguides to effect the interchange of radio fre quency energywith free space.

The invention is especially useful in the ultra-high-frequency services,such as U. F. F. television broadcasting. When used in televisionbroadcasting, both the picture and accompanying sound signal may bediplexed into the same antenna by a transmission line arrangementforming part of the feed system for the antenna and without thenecessity for separate frequency selective filters. Antennas fortelevision broadcasting which utilize coaxial and other two-wisetransmission lines are limited with respect to their power handlingcapabilities. This invention utilizes hollow pipe waveguide throughoutits construction because of the attendant higher power capability.

It is an object of this invention to provide an improved antenna forultra-high-frequency services capable of handling very high input radiofrequency power of the order of 200 kws.

Another object of this invention is to provide an omnidirectionalbroadcast antenna array of highly stable mechanical construction whichis utilizable at full power even in heavy storm-loading areas.

It is a further object of this invention to provide an antenna arrayutilizing waveguide transmission line throughout in which the frequencyof operation of the antenna can be changed from one frequency to anotherby a simple replacement of the wall of the waveguide which contains theradiating elements.

Still another object of this invention is to enable the diplexing of tworadio frequency signals to a single transmission line withoutinteraction, and feeding the diplexed signals from the single waveguidetransmission line to a number of surrounding waveguide lines which haveone wall slotted to act as antenna elements.

Yet another object of this invention is to provide means forbroadbanding one of two radio frequency signals which are fed to asingle antenna structure without interaction with the other radiofrequency signal fed to the same antenna.

In accordance with the invention, these and other objects are obtainedby an antenna system which includes a hollow pipe waveguide forming thecentral member which is utilized for bringing the radio frequency energyup to a point intermediate the ends of the array,-and a number ofsurrounding Waveguides of special configuration which have slots in oneface to effect the interchange of radio frequency energy between theguides and free space. The slotted waveguides which surround the centralwaveguide may be basically of isosceles trapezoid cross-section.Alternatively, either the inner or the outer of the broad walls of thesurrounding waveguides may be arcuate. Metal ridges are attached to theinner broad wall of the surrounding waveguides to lower the cut-offfrequency. The slots which act as the antenna elements are cut in theouter walls of the specially shaped surrounding'waveguides. The outerwalls of the surrounding waveguides may be made in the form of coverplates into which the slots are cut so that the frequency of operationmay be changed to any frequency of operation occurring over a broadfrequency band by simply changing the outer cover plate to anothercontaining differently dimensioned and differently positioned slots. Theslots may be excited by being positioned off the center line of thewalls. a

Radio frequency energy is conveyed up the central waveguide member whereit is transferred to the specially shaped surrounding guides in which itis propagated both upward and downward along the entire length of theaperture. Adjustable shorting bars are provided at the upper and lowerends of each of the specially shaped guides.

An important feature of the invention is the cross-sectionalconfiguration of the antenna structure which results from a centralwaveguide surrounded by a plurality of waveguides. This cross-sectionalconfiguration yields an antenna array structure which may be made from20 to 40 wavelengths or more long yet have high bending and flexurestrength and therefore capable of standing high wind velocities andsevere ice loading.

A more detailed description follows in conjunction with the accompanyingdrawing wherein:

Figure 1 is a side elevation of an omnidirectional antenna array inaccordance with the invention;

Figure 2 is a cross-section along the line 2-2 of Figure 1;

Figure 3 is a cross-section along the line 33 of Figure 1;

Figure 4 is a cross-section along the line 44 of Figure 1;

Figure 5 is a cross-section along the line 5-5 of Figure 1;

Figure 6 is a cross-section along the line 6--6 of Figure 1;

Figure 7 is a cross-section along the line 7--7 of Figure 1;

Figure 8 is a cross-section of loaded rectangular waveguide which may beutilized in the invention;

Figure 9 is a cross-section of loaded isosceles trapezoidal waveguidewhich may be utilized in practicing the invention;

Figures 10, 11, 12 and 13 show alternative configurations ofcross-sectional arrangements of antenna arrays embodying the principlesof the invention; and

Figure 14 is a graph utilized in explaining the invention.

Referring now to Figures 1 to 7, an antenna array constructed inaccordance with the invention contains a central waveguide 21 ofoctagonal cross-sectional configuration. The central waveguide 21 mustbe capable of supporting two orthogonally disposed dominant polarizedtransverse electric loads of propagation (TE11), and preferably shouldbe able to support a mode having circular symmetry (TMoi). Waveguides ofcircular cross-section or of equilateral polygonal cross-section havingan even number of sides (4, 6, 8, 10 etc.) fulfill these requirements.Also, coaxial transmission lines may be operated in the coaxial TE11mode as well as the TEM mode to be used as the central waveguide 21. r

The central waveguide 21 is surrounded by a number of Waveguides havinga specially shaped cross-sectional configuration. Each of thesurrounding waveguides is identical. The waveguides are denoted by thereference characters 23a through 23h. The shape and positioning of thesewaveguides 23a through 23h may be understood best by referring toFigures 2, 3, 4 and 5 as well as to Figure 1.

Figures 2, 3, 4 and 5 are cross-sectional views along thecorrespondingly numbered section lines of Figure 1 of the broad walldimension and having a-height which is a substantial proportion of thenarrow wall dim en- Becanse ot-the magnitude of the optimum diameter ofmecentral waveguide 21, rectangular or trapezoidal guides havingatwo-to-one broad-to-narrow wall dimension ratio are, too small, that is,below cut-off, at the frequencies at which the central guide 21 isdesigned to operate. The ridges 25a through 25h lower the cutofffrequency (it the surrounding waveguides 23a through 23h so that file]will eficiently transmit the frequencies which can be Wted in thecentral waveguide 21.

A; shown in Figure 2, thesurrounding waveguides 23a ml'pugh flhare'terminated at the ends of the antenna array by'metallicshort-circuiting blocks 27a through 27h. The shortcircuiting blocks 27may be positioned about MM'I 'Om the center of the last layer of slotsat each end of the antenna array.

Referring now especially to Figures 1, 3 and 4, and asmm that theantenna is being ,used for transmitting purposes, the radio frequencyenergy is propagated up the central waveguide 21 to a layer of couplingelements 29a m 29h which are used to transfer the energy from thecentral guide 21 to the surrounding rectangular guides 13d through 23h.The coupling elements 29a through Zhare shown as simple voltage probeswhich extend througha hole in the outer broad wall of the waveguide 23,.Ihrough a clearance hole in the ridge 25 and into the interior of thecentral guide 21. Other coupling means than the probes shown in thedrawing, such as, for example,

3 or slots, may of course, be used although the meehanical arrangementof the probes shownprovides a simple mechanical adjustment of the degreeof coupling between the individual surrounding guides 23a through 23!:and the central guide '21, which may be varied easily {mm the exteriorof the antenna structure. The layer of coupling elements or probes 29athrough 29h provides the-feed point for the antenna array which extends'both up and down from this point.

vFigure 3 shows a metallic short circuiting plate 31 located inthe-central guide 21 beyond the feed point (section H, Fig. 1.) from theassociated radio frequency apl'his shorting platelmay be usedfor tuningand matehing'by'altering its position in the central waveguide Z1 abovethe .feedpoint, as well as for preventing energy horn continuing on inthe central waveguide 21.

31083.3 cut in the broad wallof a rectangular waveguide may befed bymeans of probes or loops or by care- Tully'positioning such slots to oneside or the other of the center axis of the broad wall. A waveguide oftrapezoidal cross-sectional shape behaves in substantially the same wayIs 'rect'angllar guide, and ofi-center positioning of the 'ilotstooonplethe wave .in the trapezoidal guide between .the guide and .freespace isshown in Figures 1, 3 and .5. men ofl-center positioning isused, noprobes or loop couplings are requiredto excite the slots. Thedegree of slot oouplingis a function of the amount of offsetting of theslot fi'om'the center line of the broad wall.

In the embodiment of the invention shown in Figures 1 W5, the slots 33associated with atsingle specially shaped waveguide, for example the onedenoted by the be madea'pure. resistance by slightly adjusting thelengthot'ihe'individual slot. The width of the individual slots 33 m! be-usedwithin certain limits'to control theband widtheharacteristics. If theupper and lower halves of the antenna are to be fed in phase, and thedistances from the feed point to the coupling elements 29 are to beequal, the two slots adjacent to the feed point are offset on the sameside as shown in Figure 1. The distance of the center of the first layerof slots from the feed point at the coupling elements 29 may be adjustedfrom approximately 7\ /4 upwards for broadbanding and matching purposes.

All of the surrounding specially shaped waveguides 23a through 23h maybe excited in phase by propagating a mode having circular symmetry inthe central guide 21. The lowest order mode having circular symmetry isthe TM01 mode. This mode may be launched in the central guide 21 bymeans of an axial probe 35 extending into one end of the guide 21. Theprobe 35 may be an extension of the inner conductor of a coaxialtransmission line or, as shown in Figure 1, may be a probe extendingtransverse (across the narrow dimension) to a rectangular waveguide 37in which the TEm mode of propagation is present.

However, for television broadcasting purposes, the use of only the TM01mode in a cylindrical guide 21 requires that the picture and soundsignals be diplexed into a single feed line. Systems presently in usefor this diplexing operation embody frequency-selective filters. Suchfilters are critical in construction and adjustment in the ultrahighfrequency range. A preferred method of feeding the antenna array of thisinvention without the use of frequency-selective filters in thediplexing operation will now be described.

Two polarized dominant waves (for example, the TEu mode in circularguide) are excited in the central waveguide 21 orthogonally disposedwith respect to one another and in time relation. The resultant wave isa linearly polarized wave whose principal electric vector has anapparent rotation at radio carrier frequency. This is called circularlypolarized (for two equal-amplitude 'TEn waves) or rotating polarizationpropagation. The circularly polarized wave excites the voltage probes29a through 29h at the feed point with equal amplitude and progressivelyphased voltages.

Referring now to Figures 1, 5 and 6, one method of converting a linearlypolarized TEn wave to a circularly polarized wave is shown. Twooppositely disposed phaseshifting fins 39 are attached to the inside ofthe cylindrical guide 21. The phase shifting fins 39 are at an angle of45 with respect to the incident TE11 wave. For example, in Figure 6 thedirection of the electric field is shown as being vertical and the phaseshifting fins shown in Figure 5 are rotated through 45. The TEii wave ofFigure 6 may be divided into two equal orthogonally disposed components,one component perpendicular to a plane common to the two phase shiftingfins 39 and another component parallel to the same plane. The finsproduce a relative phase delay between the two components due to thedifferent loading presented to the two mponent o the IE1; W vey p perlyjus g h siz and leng o e p a e shif g fins a phase difference isproduced. These two components are in the proper time relation andspatial disposition to propagate as a circularly polarized wave.

The .phase shifting fins 39 utilized in the present invention aredifferent in design from those .of the prior art in that they occupy avery small proportion of a diameter of the central waveguide 21. Bymaking the phase shifting fins of the fo m shown in Figure 5, they maybe utilized in a circularor polygonal waveguide which propagates loworder circular modes (for example the TMui) without acting as rnodefilters for such waves. The length of such fins for a given amount ofphase shift must be longer than thoseof prior design because the amountof shift in phase per guide wavelength is much less. The ends of thefins 39 are tapered from the wall ofthe wave guide to-their full height.This taper may be a gradual taper or, for convenience in mechanicalconstruction, it may be of stepped configuration. 'If the taper of thefins is of step form, each step mayconveniently be made \g/4 in lengthtoprovide a reflectionless transition.

An incident linearly polarized wave with its principal electric vectororiented in 90 spatial relationship to the case just described, likethat, for example, shown in Figure 7 where the direction of the electricfield is horizontal rather than vertical, will produce a circularlypolarized wave having its rotational sense opposite to that of the TE11wave of Figure 6. The two contra-rotating circularly polarized waves arecompletely decoupled from each other independent of the frequency atwhich the circular waveguide is terminated in a matched load.

Since the two TE11 modes are inherently decoupled, two radio frequencysignals within the same frequency band may be propagated simultaneouslyin the guide 21 without interaction. Referring to Figures 1 and 6, arectangular waveguide 41 having its broadwalls parallel to thelongitudinal axis of the circular guide 21 may be used with a TEM] modein the rectangular guide 41 to excite a directionally polarized TE11wave in the circular waveguide 21.

Similarly, referring to Figures 1 and 7, a rectangular waveguide 43 withthe same mode of propagation, TElO, may be used to excite a TEu mode inthe octagonal central guide 21 at right angles to the other wave. Inconjunction with the phase shifting fins 39, these two modes produce twocontra-rotating circularly polarized waves in the circular waveguide 21as explained above in connection with Figures 1, 5 and 6;

The three decoupled feed points thus provided by the axial probe 35 andthe two rectangular wave guides 41, 43 allow a diplex or triplex feed ofthe antenna array of Figure 1. This feed system may employ all threemodes for triplexing three signals into the same antenna as long as theyare closely spaced in the frequency spectrum, or two signals may bediplexed and the third feed terminal terminated in an absorbing resistorfor stabilization and broadbanding purposes.

With the increasingly stringent requirements of sideband transmissionwithout phase shift arising in the radio frequency equipment, it appearsmore and more desirable to provide ultra-high-frequency broadcastantennas capable of accepting and radiating two or more radio frequencysignals without the use of frequency selective filters.

As an example, assume that it is desired to diplex a broadband picturesignal with a narrow band sound signal, the problem encountered inultra-high-frequency television transmission. The broadband picturesignal is fed to the rectangular waveguide 41 in the TEw mode to createa circularly polarized TEll wave in the circular waveguide 21. Theaccompanying sound transmission is coupled to excite the TEro mode tothe rectangular waveguide 37 and the axial probe 35 in the circularwaveguide 21 excites the TM01 mode. An absorbing resistance load is usedto terminate the other rectangular waveguide 43.

The radio frequency signal from the picture transmitter coupled to therectangular waveguide 41 is converted by the polarizing fins 39 to acircularly polarized wave which couples progressively to the probes 29to excite the surrounding waveguides in phase rotational fashion. Theslots 33 in the outer walls of the surrounding waveguides 23 produce afield which is progressively phased with regard to the several slots 33.Energy from the sound transmitter which is coupled to the axial probe 35will excite the slots 33 in an in-phase relationship.

Any picture energy which is reflected due to incorrect termination ofthe circular waveguide 21 because of antenna element mismatch or similarinconsistencies is converted by the polarizing fins 39 to a linearlypolarized wave at right angles to the incident wave and is thereforereturned to the rectangular waveguide 43 to be absorbed in the resistiveload. The radio frequency transmitter for the sound signal coupled tothe axial probe 35 is therefore decoupled from either direct orreflected picture energy.

very desirable because of the increased bandwidth over which the antennasystem offers a constant load to the transmitter and also because of theimproved isolation between the picture and sound signals.

Figure 8 shows an alternative form of loaded rectangular waveguide 45which may be used in place of the waveguides 23a through 23h of Figures1 through 5. Instead of utilizing the metal ridges 25 shown anddescribed above, a plate 47 forming a cap portion of a partial septum 49may be used to lower the cutoff frequency of the rectangular waveguideso that it will efficiently transmit frequencies which can be propagatedin an octagonal guide in which one of its broad walls forms one of thesides of the octagon.

Figure 9 is an isosceles trapezoidal waveguide 51 similar to thespecially shaped waveguides 23a through 23h of Figures 1 through 5 whichutilizes the plate and partial septum 47, 49 arrangement like that ofFigure 8. The isosceles trapezoidal waveguide 51 may be directlysubstituted for the specially shaped surrounding waveguides 23 inFigures 1 through 5 described above.

Figures 10, 11, 12 and 13 show alternative cross-sec tionalconfigurations of antenna arrays which may be used in practicing theinvention. In Figure 10, the central waveguide 21' is circular incross-section and the surrounding waveguides 23' are arcuate segments.These arcuate waveguides 23' are each loaded by metal ridges 25 likethose described above in conjunction with Figures 1 through 5.

In Figure 11, the central waveguide 21' is shown as being of circularcross-section, surrounded by waveguides 23" having an arcuate broad wall(the interchange for a common wall between the central circularwaveguide 21'), the other broad wall and the two narrow walls beingplane surfaces.

Figure 12 shows a cross-section which utilizes an octagonal centralwaveguide 21 surrounded by waveguides 23" having an arcuate outer broadwall.

Figure 13 is similar to the arrangement shown in Figure 10, except thatthe central circular waveguide 21 is filled with a dielectric medium 53to lower the cutoff frequency of waves which may be eflicientlytransmitted and thus reduce the cross-sectional size of the resultingantenna array. Some of the advantages of the arrangement shown in Figure13 are reduced wind resistance, reduced weight of the antenna arrayproper, and improved pattern circularity as will be explained in furtherdetail below.

The surrounding waveguides 23 may also be filled with a dielectricmedium 55 to lower the cut-ofl frequency of waves propagatedtherethrough to dispense with the necessity for the loading ridges 25shown in the previous figures or in conjunction with the ridgedwaveguides shown above to further reduce the size of the surroundingwaveguides.

Referring now to Figure 14, the non-circularity ratios of the horizontalfield pattern vs. antenna diameter for progressively phased antennas offour and eight slots are set forth in graphical form. It will be seenthat an antenna utilizing four axial slots has minima in the horizontalfield pattern which become somewhat troublesome if the diameter of thecylinder is larger than about 0.3%.

Since the antenna diameter for an antenna array in accordance with thisinvention is the sum of the diameter of the central waveguide 21 or 21'plus twice the height of the specially shaped waveguides 23 (or 23, 23"or 23"), it is apparent that more than four slots are needed to providea sufficiently circular pattern for reasonable range of size of theinner central waveguide 21.

Also shown on Figure 14 is a plot of the relative phase velocity, or forthe TEn mode plotted against the diameter of the central waveguide. Thediameters at which cutoff is obtained for the first three modes, TE11,TMoi and TEZl, are also indicated. A practical operating range ofapproximately 0.7). to 0.95). is chosen for the inner cylinder diameter,being limited at the lower (the same material.

therea lly increa in h s l t and. at th amtarl-b! the un e ired 2 1 modflsmr. ta th ei t x al la rran e t 1? ie We 1, in which therectangularguide height to width is cng to two, the corresponding antenna m are1.07) to 1. 4 for this range of central calwsuyeguide eine. From Figure14, it can be m non-circu r t rat c in of about with his n e o v ue ivthe en ral w e u 11 or h a to increase its cutolf wavelength, as der!"jg egnjunction with Figure 13, the over-all cylin- 1;-.:. i made Smallerthan the above rep resentative values, the antenna can be made to have apatern wh ch we e nea l approach absolute circularity M rhea flames, animportant pract cal advantage 1s secured bran nngennaof the design shownin Figure 1 wherein waveguide-s through 23/1 are made of U .2 qltannels,When these individual channels are assembled, the central waveguide 21of octagonal crossthe .metal vanes forming the narrow walls of thespecially shaped waveguide and the ridges 25 form the m mqll oi the.antenna assembly. This portion, as-

the specially shaped surrounding waveguides zfigttju'ough I: have coverplates, may be operated over a egngiderghle portion of the U. H. F.range without change. a given U. F. television channel the slots 33 arecutin the cover plates forming the outside broad walls of {hemqnrldingwaveguides 23a through h. antenna array of this invention hasother advantpgee an well, some of which are: a very strong mechanicgionis obtained due to the radial vanes which m walls of the speciallyshaped waveguides 23; the array is fed at or near the center, which m anantenna having good bandwidth characteristics Q9 beam due to change infrequency; and no pmtrudingappendages app ar on the outer surface of the39. .01 .more kilowatts of ultrahigh-frequency W, 88!! .Bhould be notedthat with eight specially m 2 30 through 23h, each of thesurguidesneedbe capable of handling only /8 of the total average inputpower.

In an actual embodiment built in accordance with the m and successfullytried out in practice, an

new for serviu: on U. H. F. television channel 73 $18 4824 megacycles)had the following dunen- I'U: EBB central waveguide 21 was of octagonalcon- :as ghown inFigures 1 through 7 and had a raill hmrits center axisorthogonal to each side of the 6.72". The surrounding specially shaped23 hadan inside dimension across the outer lmad wall of 6.94" and adepth from the inside of the mlenltmd wall .to .the other broad wall of2.64". The new were 21 ,6 5 wide and had a clearance from the outerbroad wall of .63" with the corners near the outer host wal having aradius of The angle of the lIImwwIlls-to thebroadwalls of the isoscolestrapezoidal m were 167%" and the length of the narrow wallsflidlmatitute the .other broad walls were fabricated of-1hlflteatfluminum. The slots were cut into theouter m Mend t e f l w nPe i t mg i temately on one side or the other of the center line of Theouter cover plates' fit tl snesi llv ap d suncunsiins ave uides 23 by adi tance '.Q.45 to the center 9f the slot. The center es of t e nwbssl?t th cc erot t e fi t ad a ent an el sl ts 3-34 9 cash side w s 9- T erew 12 a'y of lots ea h s de of t e ter feed point, making a total of 24layers of eight slots per layer. The. circularly polarized fins 39 werepositioned between the feed point at the probes 29 and the nearestrectangular Wa uide 41 nd were o s epped o fi u The tal length of thefins was ewe with the first step bein in height and t e secon st p /4 orWe" ro the end of the first step) being 4' in height. The fins 39 were 4/2" wide, and were mechanically and electrical: 1 at h d t es d wall ofthe. t gonal ui Th nt r a ten a ray was nc se y a po welded fiberglasscover of 8 sections, averaging about 30. inches in length and having anoverlap section of about one inch. This cover protects the antenna fromrain, snow and ice, and further has the advantage of presenting a smoothcircular cylindrical exterior to reduce local Will urbule c What I claimis:

1. An antenna comprising a transmission line having an enclosing sidewall, a plurality of waveguides surrounding said transmission line, eachof said surrounding waveguides having an nter wall oppositely disposedrelative to said enclosing side wall, each of said outer walls havingmeans adapted to interchange energy between said hr t siin wav uid s andree p elements associated with each of said surrounding waveguidescoupling said transmission line with each of said surrounding Wa eguidesfor transferring radio frequency energy be tween said transmission lineand said surrounding waveuides 2. An antenna comprising a transmissionline having an enclosing side wall, a plurality of indiyidual waveguidessurroundingsaid transmission line, each of said r un n wave uides h vinan o e wall opp disposed relative to said enclosing side wall, each saidouter wall having a slot therein adapted to interchange energy betweensaid surrounding waveguides and free space, coupling means between eachof said surrounding waveguides and said transmission line adapted totransfer radio frequency energy between said transmission line and saidsurrounding waveguides.

-3. An antenna comprising a hollow pipe waveguide having an enclosingside wall, .a .plurality' of surrounding waveguides each having twobroad walls and two narrow walls, one of said broad walls of each ofsaid surrounding guides .being the enclosing side wall of said hollowpipe waveguide, the other broad walls each having a slot therein adaptedto interchange energy between said surrounding wayeguides and freespace, coupling element means extending from the interior of .each ofsaid surrounding waveguides through apertures in said enclosing sidewall into ,the interior of said hollow .pip'e waveguide {9r transferringradio frequency energy between'said hollowpipe waveguide and saidsurrounding waveguides.

,4. An antenna QOmprising a hollow pipe waveguide having .an enCIQSing.Side wall, a plurality of surrounding waveguides each having two broadwalls and two narrow walls, one of said walls being the outer wall .andopposite- 1y disposed relative to said hollow pipe waveguide, each ofsaid surrounding waveguides having means adapted to interchange energybetween said surrounding waveguides and freespace, coupling elementsassociated with each of said surrounding waveguides extending throughapertures in said enclosing side wall into the interior of said hollowpipe waveguide for transferring radio frequency en ergy between saidhollow pipe waveguide and said surrounding waveguide s.

5 antenna comprising a hollow pipe waveguide having an enclosing sidewall and capable of supporting two .sli es ianal q a izad rthq enal ,siee d Waves) a plurality of surrounding waveguides each having two broadwalls and two narrow walls, one of said broad walls of each of saidsurrounding guides being the enclosing side wall of said hollow pipewaveguide, the other of said broad walls having a plurality of slotstherein adapted to interchange energy between said surroundingwaveguides and free space, coupling elements associated with each ofsaid surrounding waveguides extending through apertures in saidenclosing side wall into the interior of said hollow pipe waveguide fortransferring radio frequency energy between said hollow pipe waveguideand said surrounding waveguides.

6. A slotted waveguide antenna adapted to interchange energy betweenitself and free space comprising a central hollow pipe waveguide havingan enclosing side wall and capable of supporting two directionallypolarized orthogonally disposed waves, a plurality of surroundingwaveguides each having two broad walls and two narrow walls, one of saidbroad walls of each of said surrounding guides being the enclosing sidewall of said hollow pipe waveguide and having a ridge extending theentire length thereof occupying the major proportion of the dimensionbetween said broad walls, the other of said broad walls having aplurality of slots therein displaced from the center line of said broadwall and exposed to ambient free space, coupling elements extending fromthe interior of said surrounding waveguides through apertures in saidenclosing side wall into the interior of said hollow pipe waveguide fortransferring radio frequency energy between said hollow pipe waveguideand said surrounding waveguides, said surrounding waveguides extendingaway from said coupling elements in both directions along the length ofsaid hollow pipe waveguide.

7. A slotted waveguide adapted to interchange energy between itself andfree space comprising a central hollow pipe waveguide having anenclosing side wall and capable of supporting two directionallypolarized orthogonally disposed waves, a plurality of surroundingwaveguides each having two broad walls and two narrow walls, one of saidbroad walls of each of said surrounding guides being the enclosing sidewall of said hollow pipe waveguide, the other of said broad walls havinga plurality of slots therein displaced from the center line of saidbroad wall and exposed to ambient free space, coupling elementsextending from the interior of said surrounding waveguides throughapertures in said enclosing side wall into the interior of said hollowpipe waveguide for transferring radio frequency energy between saidhollow pipe waveguide and said surrounding waveguides, said surroundingwaveguides extending away from said coupling elements in both directionsalong the length of said hollow pipe waveguide, and means to couplefurther waveguide means to said hollow pipe waveguide at a point remotefrom said coupling elements with a circularly polarized Wave in theportion adjacent said coupling elements.

8. A slotted waveguide antenna adapted to interchange energy betweenitself and free space comprising a central hollow pipe waveguide havingan enclosing side wall and capable of supporting two directionallypolarized orthogonally disposed waves, a plurality of surroundingwaveguides each having two broad walls and two narrow walls, one of saidbroad walls of each of said surrounding guides being the enclosing sidewall of said hollow pipe waveguide and having a ridge extending theentire length thereof occupying the major proportion of the dimensionbetween said broad walls, the other of said broad walls having aplurality of slots therein displaced from the center line of said broadwall and exposed to ambient free space, coupling elements extending fromthe interior of said surrounding waveguides through apertures in saidenclosing side wall into the interior of said hollow pipe waveguide fortransferring radio frequency energy between said hollow pipe waveguideand said surrounding waveguides, said surrounding waveguides extendingaway from said coupling elements along the length of said hollow pipewaveguide, and further waveguide means cooperating with said hollow pipewaveguide in a portion remote'from said coupling elements to couple twocontra-rotating circularly polarized waves between the portion adjacentsaid coupling elements and said further waveguide means.

9. A waveguide antenna system comprising a central waveguide having anenclosing side wall, a plurality of surrounding waveguides each havingtwo broad walls and two narrow walls, one of said walls of each of saidsurrounding guides being a portion of the enclosing side wall of saidcentral waveguide, antenna elements coupled to a wall opposite said onewall to interchange energy between said surrounding waveguides and freespace, means for coupling said surrounding wave guides to said centralwaveguide, further transmission line means cooperating with said centralwaveguide to couple two contra-rotating circularly polarized wavesbetween a portion adjacent said coupling elements in said centralwaveguide and said further transmission line means, and additionalcoupling means cooperating with said central waveguide to couple a modehaving circular symmetry in said central waveguide.

10. A system for radiating the energy from two transmitters comprising,a central transmission line having an enclosing sidewall and beingcapable of supporting two orthogonally disposed directionally polarizedwaves and a wave having circular symmetry, a first input transmissionline connected to said central transmission line to couple energy from atransmitter to a linearily polarized wave in said central transmissionline, a second input transmission line connected to said centraltransmission line to couple energy from another transmitter to excite amode therein having circular symmetry, a plurality of waveguidessurrounding a portion of said central transmission line, each of saidsurrounding waveguides having an outer wall in spaced relation with theenclosing side wall of said central transmission line, said outer wallhaving slots therein adapted to couple energy from said surroundingwaveguides to free space, and elements associated with each of saidsurrounding waveguides coupling energy from said central transmissionline to said surrounding waveguides.

11. A system as defined in claim 10, and in addition, an outputtransmission line connected to said central transmission line inorthogonal relation with said first input line to couple a reflectedlinearily polarized wave therefrom, and phase shifting fins disposedwithin said transmission line.

References Cited in the file of this patent UNITED STATES PATENTS2,599,753 Fox June 10, 1952 2,658,143 Fiet et a1 Nov. 3, 1953 2,668,191Cohn Feb. 2, 1954 2,679,590 Riblet May 25, 1954 2,713,151 Farr July 12,1955 OTHER REFERENCES Proceedings of the I. R. E., October 1936, page1326, copy in Scientific Library.

